What are the implications of having a Follicle-Stimulating Hormone (FSH) level less than 1?

From the Guidelines

A Follicle-Stimulating Hormone (FSH) level less than 1 typically indicates hypogonadotropic hypogonadism (HH), which requires further evaluation to determine the underlying cause and appropriate treatment. This condition is characterized by deficient luteinizing hormone (LH) and FSH secretion, leading to disrupted spermatogenesis and low testosterone levels 1. The patient should be evaluated to determine the etiology of the disorder and treated based on diagnosis, which may involve referral to an endocrinologist or male reproductive specialist 1.

Possible Causes and Investigations

Possible explanations for a low FSH level include:

• Hypothalamic dysfunction
• Pituitary disorders
• Genetic conditions like Kallmann syndrome
• Functional suppression from conditions like anorexia nervosa, excessive exercise, or stress Additional testing should include:
• Other pituitary hormones (LH, prolactin, TSH)
• Sex hormones (estradiol or testosterone)
• Potentially brain imaging to evaluate the pituitary and hypothalamus 1

Treatment Options

Treatment depends on the underlying cause and the patient's goals, particularly regarding fertility. For those seeking fertility, medications like:

• Pulsatile GnRH
• Gonadotropins (FSH/LH)
• Clomiphene citrate may be prescribed 1 The specific treatment regimen would be tailored to the diagnosis and individual circumstances. For example, patients with HH may be treated with exogenous gonadotropins or pulsatile GnRH to initiate and optimize sperm production 1.

Importance of Specialist Evaluation

Low FSH alone is not a complete diagnosis but rather a finding that requires comprehensive evaluation by an endocrinologist or reproductive specialist. Early referral to a specialist is crucial to determine the underlying cause and develop an effective treatment plan, which may involve a combination of medical and surgical interventions 1.

From the Research

Implications of Low FSH Levels

Having a Follicle-Stimulating Hormone (FSH) level less than 1 can have several implications, including:

• Infertility issues, as FSH plays a crucial role in the development of follicles in the ovaries and sperm production in the testes 2
• Decreased oocyte yield, even in patients with normal Anti-Müllerian Hormone (AMH) and Antral Follicle Count (AFC) levels 3
• Potential need for FSH replacement therapy to stimulate follicular growth and improve fertility outcomes 2

FSH Levels and Fertility Outcomes

Research suggests that FSH levels can be predictive of fertility outcomes, including:

• Pregnancy rates, with lower FSH levels associated with higher pregnancy rates in some studies 4
• Ovarian response to stimulation, with high FSH levels potentially indicating a poorer response to fertility medications 3
• Live birth rates, which may be affected by FSH levels, although the relationship is not always clear-cut 5

FSH Replacement Therapy

FSH replacement therapy, such as human menopausal gonadotropin (hMG), can be effective in improving fertility outcomes in individuals with low FSH levels, including:

• Increasing sperm concentration and motility in men with isolated FSH deficiency 2
• Stimulating follicular growth and improving oocyte yield in women with low FSH levels 2

Starting Doses of FSH

The optimal starting dose of FSH for fertility treatment is still a topic of debate, with some studies suggesting that:

• Lower starting doses of FSH may be more beneficial than higher doses in certain populations, such as those with moderate AMH levels 6
• Individualized ovarian stimulation protocols based on factors like age and ovarian reserve can optimize the chances of obtaining mature oocytes 6